Solenoids are frequently used to inject fuel into automotive engines, to control electronic transmissions, and sometimes to actuate brakes. All such solenoids use a solenoid driver that causes current to be injected into the solenoid's coil at preselected times in order to control the position of the solenoid armature and hence the opening and closing of the solenoid coil.
In many applications, it is desirable that the closure of the solenoid coil can be detected accurately. Closure detection allows, for example, verification of the operation of the solenoid, fault diagnosis, and the power dissipation in the load can be reduced by adaptively controlling the coil energise time to the minimum required for the solenoid armature to move. Accurate closure detection has particular further advantages for automotive injector solenoid coils. By detecting the closure of the injector coil, mechanical lags in the injector system can be measured and compensated for thereby improving engine timing.
The benefits from closure detection are well known, however, arrangements for implementing closure detection have so far been significantly expensive.
European patent application no. EP-A-0400389 discloses a solenoid closure detection arrangement that uses the fact that as the solenoid armature moves towards the closed position, the solenoid's inductance increases which increases the decay time of the current in the coil. The arrangement therefore detects closure of the solenoid by detecting the increase in decay time.
It is therefore desirable to provide an improved method for detecting closure of a solenoid coil which is simpler and less expensive to implement.